Recently wind turbines have been designed to harvest the kinetic energy from the wind and convert this kinetic energy into electrical energy. The preferred type of wind turbine for electricity generation applications is a horizontal axis wind turbine (HAWT). The size of wind turbines and constituting components like blades grow up quickly. As blades grow larger, the amount of reinforcement increases in a logarithmic progression. Size and cost of blades can be reduced using rotor/blade supporting means.
WO/1986/002701A1 discloses a rotor system comprising some securing members that are connected to outermost part of blade roots and support the variable-pitch blades on the rotor in a stable manner without using heavy and expensive bearing means. The problem of applying the solution described in WO/1986/002701A1 to a large wind turbine is that the securing mechanism do not support the main part of blades thus weight and cost of blades are high.
WO 2007/135391 describes a turbine blade support assembly that comprises a central hub and a plurality of carrying members extends outwardly from the central hub. A respective subsidiary hub is provided on each of the carrying members for securing a respective turbine blade to each carrying member. A plurality of support members is provided to support the carrying members. The problem of this invention is that the securing formation supports the subsidiary hubs only and turbine blade are not supported and can be heavy and expensive in a large wind turbine rotor. This problem can be managed using longer carrying members and shorter blades. But this configuration causes a higher aerodynamic drag and lower aerodynamic efficiency of the rotor system.
EP 2 112 372 A1 discloses a horizontal axis wind turbine rotor that each blade is supported on the leeward side and possibly windward side by some supporting means having a first end and a second end. The first end being connected to the blade at a first mounting point positioned in a radial distance from the horizontal axis, and the second end being connected to a second mounting point at a rotatable part of the wind turbine, the second mounting point being positioned in an axial distance from the rotor plane on the leeward or windward side of the rotor. The problem of this invention is that the supporting means generate extra noise as well as extra drag that reduce rotor aerodynamic efficiency. Moreover during the variation of blade pitch angle, internal load of supporting means change and restrict securing effect of supporting means. Meanwhile twisting effect of supporting member loads on the blade should be considered.
EP1365106A1 discloses a rotor system comprising a rotatable supported central hub, and a plurality of blades formed on the central hub at a plurality of circumferential locations and protruding radially outward. The blades each include a first blade element extending radially outward from a first attachment position on the central hub, a second blade element extending radially outward from a second attachment position on the central hub, and a third blade element connecting the tips of the first and second blade elements. The problem of applying this solution is that the blade tip is not very effective point for connecting the first and second blade portions to improve stiffness of blades in a large wind turbine with large and slender blades. Also the blade pitch variation is not possible thus this invention cannot be used in the large and high performance wind turbines.
It is well known from the aircraft industry that aeroplanes built with two joined wings show normally higher aerodynamic efficiency (low induced and airfoil drags) and lower structural weight due to supporting effect of joined wings. An objective of this invention is to provide a similar joined blade rotor system to improve aerodynamic efficiency and to reduce structural weight of the rotor system.
Hence, an improved blade rotor system would be advantageous, and in particular a more efficient and/or reliable blade rotor system would be advantageous.